Oblique Angle Deposition of HfO2 Thin Films: Investigation of Elastic and Micro Structural Properties

TL;DR

This study investigates how the elastic and microstructural properties of HfO2 thin films vary with oblique angle deposition, revealing significant changes in stiffness and density related to deposition angle, which impacts their stability and optical applications.

Contribution

It provides new insights into the relationship between deposition angle and both elastic and microstructural properties of HfO2 thin films, using advanced microscopy and measurement techniques.

Findings

Indentation modulus increases from 42 GPa at high angles to 221 GPa at normal deposition.

Density and elastic modulus both decrease parabolically with increasing deposition angle.

Microstructural analysis confirms the density variation through FESEM imaging.

Abstract

Oblique angle deposition of oxides is being famous for fabricating inhomogeneous thin films with variation of refractive index along thickness in a functional form. Inhomogeneous layers play a key role in the development of rugate interference devices for photo-physical applications. Such obliquely deposited thin films show high porosity which is a critical issue related to their mechanical and environmental stability. Hence, it is important to investigate elastic properties of such film in addition to optical properties. Using atomic force acoustic microscopy, we report indentation modulus of HfO2 thin films deposited at angles 80, 68, 57, 40 and 0 degree with normal to substrate plane on Si (100) substrate. Such films were measured to have indentation modulus of 42 GPa for extreme obliquely deposited film and indentation modulus increases with decrease in angle to become highest with a value of 221 GPa for normally deposited films. We also report microstructural properties and density of films measured by FESEM and grazing angle X-ray reflectometer respectively. Both indentation modulus and density depict a parabolic decreasing behavior with angle of deposition. Variation of density is again confirmed by FESEM cross-sectional morphology of such films.